1. Field of the Invention
The present invention relates in general to a landing gear damper and, more particularly, but not by way of limitation, to a landing gear damper for a helicopter which allows for appropriate ground resonance performance.
2. Brief Description of Related Art
Aircraft landing gears, such as landing gears for airplanes, helicopters, and other aircraft are typically equipped with hydraulic damper systems and struts to absorb forces during aircraft landing and to help support the aircraft while on the ground. Helicopter landing gears absorb the energy from landings through damper motion and elastic deformation of struts.
Helicopter landing gears have unique design requirements. Military helicopter landing gears are required to function in vertical sink speeds ranging from 8 ft/sec limit landing to 42 ft/sec crash landing conditions. To provide protection to the airframe, other aircraft components, and cargo, multistage shock struts with controlled mechanical failures are utilized. Some civil helicopters utilize shock struts in combination with skid gears. Although the sink speed ranges for civil helicopters are less stringent than those for military helicopters, ground resonance, static ground position, structural and economic considerations are still relevant.
One critical design requirement for helicopters is static ground clearance, or the ability of the landing gear to support the helicopter's weight without “bottoming out.” Static ground clearance is one of a myriad of design requirements for helicopter landing gears, for example, energy absorption capability, load factor, ground resonance and the like. The landing gear damper is one of the key components most influenced by design requirements.
Static ground clearance for helicopters can be increased by reducing damper stroke. Typically, this is facilitated by utilizing a nitrogen containing damper in which the amount of nitrogen in the damper system is increased. Nitrogen containing dampers are replete with drawbacks. For example, any leakage of nitrogen (a common problem with current systems) causes adverse performance of the damper, such as ground resonance problems.
Thus, a need exists for a helicopter landing gear damper which reduces the need for maintenance of the same and provides for enhanced performance, and reduced ground resonance. It is to such an apparatus that the present invention is directed.